The invention relates to a side-channel pump and particularly to end covers which close opposite axial ends of the pump and provide the side channels therefor.
Such a side-channel pump has a housing, a drive means and at least one pump mechanic which pumps liquid from an inlet of the pump mechanism to the outlet of the pump mechanism, the pump mechanism including opposite end covers with side-channels and a rotatable impeller between the end covers. The impeller has blade rims in both axial walls that are joined together and each end cover has a side channel that tapers in the running direction of the impeller.
Such a side-channel pump is disclosed in DE 197 04 403 A1 which has means to improve pump efficiency and reduce noise generation. In this respect, the impeller is made of an injection-molded plastic with a metal reinforcement.
A pump is also disclosed in DE 196 34 253 A1 which has a ceramic disc between the impeller and the side-channel cover, in which a disc slot is made that corresponds to the shape of the spiral side channel. The side channel is completed by a recess provided in the end cover. The ceramic disc has the disadvantage that it is subject to inaccuracies due to shrinkage of the ceramic material during the manufacturing process. This prevents precise production which leads to variations in the cross-sectional surface of the side channel. Hence, a cross-sectional surface that is optimal for good efficiency cannot be precisely achieved without expensive post-processing operations. However, according to the citation the ceramic material is desirable for the disc since it decreases the wear between the side-channel cover and the impeller. Otherwise, the service life of the side-channel pump could be adversely affected.
Thus, there is a need for measures that are suitable for mass production, which reduce the fluctuations in the cross-sectional surface of the side channel without increasing the wear between the side-channel cover and the impeller.
This object is achieved in side-channel pumps of the type described above by making the end cover as a composite structure of a ceramic disc and a plastic unit, the ceramic disc being provided with a slot in which the plastic unit is fitted and includes the side channel.
In an advantageous embodiment, the ceramic disc has a peripheral shoulder facing away from the impeller and the plastic unit has a flange seated at the shoulder on the ceramic disc.
In an alternative embodiment, the plastic unit is integrally joined to the pump housing.
In accordance with the invention, the ceramic disc is smooth on the surface facing the impeller and is rough on all of the other surfaces, particularly the surface facing away from the impeller. Advantageously, the surface of the ceramic disc that faces the impeller is made smooth by honing or lapping. The functionally adapted form of the side channel is obtained by making the side channel in the plastic unit tapered in its cross section by reducing the width and/or depth of the side channel. It is also advantageous if the plastic unit is comprised of a non-swelling, form-stable plastic.
If a part of the plastic unit completely or partially occupies the peripheral shoulder provided in the ceramic disc, this is advantageous, in that the thickness of the part of the plastic unit that projects into the peripheral shoulder is small in comparison to the thickness of the ceramic disc.
It is possible to combine the advantages of ceramic and plastic materials by means of this invention for a side-channel pump by separating the functions required for the side-channel cover respectively by the ceramic disc and the plastic unit. The composite structural unit can thus be used also for direct bearing support of the drive shaft without additional components, due to the properties of the plastic material.
The requirements with respect to manufacturing accuracy for the slot in the ceramic disc are not particularly high, since the slot is occupied by the plastic unit. Since the side of the ceramic disc facing the impeller is made smooth, for example, by honing or lapping, the advantage of little wear is maintained. For a high resistance to wear of the side-channel pump, it is recommended to form the plastic unit of thermosetting or thermoplastic material. The wear between the side-channel cover and the impeller is thus minimized.
Because the surfaces of the ceramic disc are rough, with the exception of the surface facing the impeller, they permit the plastic unit that is injection molded onto the ceramic disc, to bind particularly effectively with the ceramic disc. Stability is considerably improved by providing the ceramic disc with suitable means at the periphery on the side facing the impeller, for example, teeth, shoulders, etc. Then, the peripheral flange of the plastic unit can engage the peripheral shoulder at the outer periphery of the ceramic disc, so that the ceramic disc is completely attached in the plastic unit. In this way, it is possible to arrange the thus formed side-channel cover in the side-channel pump, such that an axial force is not absolutely necessary in order to hold the ceramic disc and the plastic unit together.
The shape of the side channel in the plastic unit can be formed with high accuracy during the injection-molding process by an appropriately shaped tool, whereby the accuracy of the side channel is considerably improved. The fluctuations in the cross-sectional surface of the side-channel in the prior art construction thus will be clearly reduced.
The production of the side-channel pump by means of this procedure is particularly suitable for mass production, since processing steps that are time-consuming and expensive can be omitted. The cross-sectional tapering of the side channel is formed during the injection-molding process with high accuracy by modifying the width and/or depth of the channel in the plastic unit so that subsequent processing is unnecessary. The ceramic disc only involves its basic shape and thus is simple to produce.